Catalyst and method for synthesis of lactic acid and its derivatives

ABSTRACT

A catalyst for synthesis of lactic acid and it derivatives is provided. The catalyst includes SnY2.mH 2 O and at least one of NH 4 X or quaternary ammonium salts, wherein X and Y are selected from F—, Cl—, Br—, I—, CH 3 SO 3 —, C 6 H 5 SO 3 —, CH 3 C 6 H 4 SO 3 — or CN—, m represents an integer of 1 to 15. A method for synthesis of lactic acid and it derivatives with the above catalyst is also provided. By using the above catalyst and method, it is capable of converting carbohydrate-containing raw material to lactic acid and its derivatives directly in a more efficient and economical way.

FIELD OF THE INVENTION

This invention generally relates to synthesis of lactic acid and itsderivatives, and more particularly to a catalyst and a method forsynthesis of lactic acid and its derivatives.

BACKGROUND OF THE INVENTION

Glucose, sugarcane, starch, and celluloses are the most abundantrenewable carbon sources found naturally on the earth. The high contentof oxygenated functional groups in these carbohydrates has advantages inmaking use of them to produce fundamental chemicals. In particular,these carbohydrates are the most attractive feedstocks for intermediatechemical production in a sustainable way without emitting CO₂.

Theoretically, two moles of lactic acid could be obtained from one moleof hexose either by fermentation or by catalytic reaction. Lactic aciditself is a monomer for the biodegradable polylactate synthesis. Lacticacid and its derivatives (such as alkyl lactates and polylactate) couldact as platform compounds for the synthesis of other carbon-3 buildingblocks, such as propylene glycol, acrylic acid, and allyl alcohol forthe productions of polymers.

Lactic acid is produced by the fermentation of glucose in presentchemical industry. FIG. 1 shows the scheme for lactic acid and itsderivatives preparation according to a commercial fermentation process.In the fermentation process, the concentration of lactic acid in theobtained water solution is very low. For example, the weight ratio ofthe lactic acid may be less than 10%. In addition, to isolate the lacticacid from the water solution, Ca(OH)₂ should be added into the watersolution, and Ca(OH)₂ reacts with lactic acid thereby producing calciumlactate solid. Then, the calcium lactate solid is separated and addedinto H₂SO₄ solution. Accordingly, lactic acid is obtained, and CaSO₄solid precipitates in the lactic acid. Obviously, in the fermentationprocess described above, huge amounts of waste water and CaSO₄ solidwaste was produced, and only glucose can be used as the feedstock.Lactic acid could be produced from glucose in large scale (120,000tons/year) in the existing fermentation processes. However, thebiological processes generally suffer from low reaction rates and lowproduct concentration (in water), resulting in long reaction times,larger reactors, and high energy consumption in the product purificationprocess (Fermentation of Glucose to Lactic Acid Coupled with ReactiveExtraction: Kailas L. Wasewar, Archis A. Yawalkar, Jacob A. Moulijn andVishwas G Pangarkar, Ind. Eng. Chem. Res. 2004, 43, 5969-5982).

It is known that, in the presence of aqueous alkali hydroxides,monosaccharides can be converted to lactic acid (R. Montgomery, Ind.Eng. Chem., 1953, 45, 1144; B. Y. Yang and R. Montgomery, Carbohydr.Res. 1996, 280, 47). However, the stoichiometric amount of base(Ca(OH)₂) and acid (H₂SO₄) in the lactic acid recovery process would beconsumed and, therefore, the stoichiometric amount of salt waste wouldbe produced.

Although the commercial fermentation approach can produce large scalelactic acid, it only uses starch as a feedstock and the starch must beprehydrolyzed (or through fermentation) to glucose in advance. Thefermentation process produces large amounts of waste water and solidwaste (CaSO₄). And the fermentation process for producing lactic acidincludes many steps, which consume substantial amounts of energy. Theinfrastructure of the fermentation process is very complicated anduneconomical.

SUMMARY OF THE INVENTION

It is desired to have a process to convert carbohydrate-containing rawmaterial to lactic acid and its derivatives in a more efficient andeconomical way.

A catalyst for synthesis of lactic acid and it derivatives, includesSnY₂.mH₂O and at least one of NH₄X or quaternary ammonium salts, whereinX and Y are selected from F—, Cl—, Br—, I—, CH₃SO₃—, C₆H₅SO₃—,CH₃C₆H₄SO₃— or CN—, m represents an integer of 1 to 15.

A method for synthesis of lactic acid and its derivatives is alsoprovided. First, a mixture is prepared, which includes: at least onecarbohydrate-containing raw material, at least one alcohol, at least onecatalyst, and at least one solvent, wherein the catalyst comprisingSnY₂.mH₂O and at least one of NH₄X or quaternary ammonium salts, whereinX and Y are selected from F—, Cl—, Br—, I—, CH₃SO₃—, C₆H₅SO₃—,CH₃C₆H₄SO₃— or CN—, m represents an integer of 1 to 15. Then, themixture is heated to obtain lactic acid and its derivatives.

By using the above described catalyst and method, it is capable ofconverting carbohydrate-containing raw material to lactic acid and itsderivatives directly, and pure lactic acid and its derivatives can beobtained after a simple distillation process. Compared with conventionalcommercially employed fermentation process, the newly proposed processhas the advantages of simplified steps and reactors, no need to use hugeamounts of acid and base to purify the products, low energy consumptionand no solid waste production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the scheme for lactic acid preparation according to acommercial fermentation process.

FIG. 2 shows the scheme of a method for synthesis of lactic acid and itsderivatives in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The detailed descriptions of the present invention set forth below inconnection with the examples are preferred embodiments of the presentinvention, but the present invention is not limited to the embodimentsand forms described hereinafter.

This disclosure provides a catalyst for synthesis of lactic acid and itsderivatives. The catalyst includes SnY₂.mH₂O and at least one of NH₄X orquaternary ammonium salts, wherein X and Y are selected from F⁻, Cl⁻,Br⁻, I⁻, CH₃SO₃ ⁻, C₆H₅SO₃ ⁻, CH₃C₆H₄SO₃ ⁻ or CN⁻, m is the number ofthe crystallization water, which represents an integer of 1 to 15.

X and Y can further be selected from F—, Cl—, Br—, I—, or CN—.

The cation of the quaternary ammonium salts is an organic cation thathas the general formula of (NR₁R₂R₃R₄)⁺, in which, the R₁, R₂, R₃, andR₄ are alkyl groups with formula of C_(n)H_(2n+1), wherein n representsan integer of 1 to 30.

In addition, a mass ratio of the at least one of NH₄X or quaternaryammonium salts to the SnY₂.mH₂O is in a range from 1:2 to 5:2. Forexample, the ratio may be 1:2, 70:33, 2:1 or 5:2. It is understood thatthese are only illustrative examples, but their disclosure is notintended to limit the values of the ratio.

By using the above described catalyst, it is capable of convertingcarbohydrate-containing raw material to lactic acid and its derivativesdirectly, and pure lactic acid and its derivatives can be obtained aftera simple distillation process. Compared with conventional commerciallyemployed fermentation process, the newly proposed process has theadvantages of simplified steps and reactors, no need to use huge amountsof acid and base to purify the products, low energy consumption and nosolid waste production.

This disclosure further provides a method for synthesis of lactic acidand its derivatives. Referring to FIG. 2, in this method,carbohydrate-containing raw material, the above described catalyst, analcohol and a solvent are added into a reactor, and then heated to carryout the reaction. The obtained solution is distillated to obtain lacticacid and its derivatives, and the catalyst can be reused.

The alcohol is selected from the group consisting of monohydricalcohols, dihydric alcohols, and trihydric alcohols. Further, themonohydric alcohol is selected from at least one of methanol, ethanol,1-propanol, 2-propanol, 1-butanol, 2-butanol, and tert-butanol. Thedihydric alcohol is selected from the group consisting of ethyleneglycol, 1,2-propanediol, and 1,3-propanediol. The trihydric alcohol isglycerol.

A mass ratio of the alcohol to the carbohydrate-containing raw materialis greater than 1, and in other embodiments, the mass ratio of thealcohol to the carbohydrate-containing raw material is further greaterthan 3:2.

The solvent, for example, is a polar solvent, such as water, alcohols,the methyl esters of C8 to C22 fatty acids, or mixtures thereof, whichcould dissolve the catalyst to form a homogeneous catalyst solution.

A reaction temperature of the heating step is between 25 and 200° C.,and more preferably, the reaction temperature of the heating step isbetween 25 and 180° C.

In addition, the reaction temperature can be further adjusted accordingto different composition of the carbohydrate-containing raw material.

In a specific embodiment, the carbohydrate-containing raw material iscellulose and the reaction temperature is between 80 and 180° C.; morepreferably, the reaction temperature is between 80 and 160° C.

In a specific embodiment, the carbohydrate-containing raw material isstarch and the reaction temperature is between 80 and 180° C.; morepreferably, the reaction temperature is between 80 and 160° C.

In a specific embodiment, the carbohydrate-containing raw material issucrose or glucose and the reaction temperature is between 25 and 180°C.; more preferably, the reaction temperature is between 25 and 140° C.

By using the above described method, it is capable of convertingcarbohydrate-containing raw material to lactic acid and its derivativesdirectly, and pure lactic acid and its derivatives can be obtained aftera simple distillation process. Compared with conventional commerciallyemployed fermentation process, the newly proposed process has theadvantages of simplified steps and reactors, no need to use huge amountsof acid and base to purify the products, low energy consumption and nosolid waste production.

Example 1 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.100 g of NH₄Cl were addedinto a reactor (inside volume 12.0 mL) as catalyst. 6.0 mL of methanol,0.200 g of water, and 0.200 g of sucrose were added into a reactor, andthen the reactor was sealed and heated to 130° C. under stirring tocarry out the reaction (from 25 to 130° C. within 25 min) The reactionwas carried out at 130° C. for 2 h. The product was analyzed by gaschromatograph with thermal conductivity detector (GC-TCD). The yield ofmethyl lactate is 45%.

Example 2 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of NH₄Cl were addedinto a reactor (inside volume 12.0 mL) as catalyst. 6.0 mL of methanol,0.200 g of water, and 1.00 g of sucrose were added into a reactor, andthen the reactor was sealed and heated to 130° C. under stirring tocarry out the reaction (from 25 to 130° C. within 25 min) The reactionwas carried out at 130° C. for 2 h. The product was analyzed by GC-TCD.The yield of methyl lactate is 33%.

Example 3 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of[N(CH₃)₃(n-C₁₈H₃₇)]Cl were added into a reactor (inside volume 12.0 mL)as catalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g ofsucrose were added into the reactor, and then the reactor was sealed andheated to 130° C. under stirring to carry out the reaction (from 25 to130° C. within 25 min) The reaction was carried out at 130° C. for 2 h.The product was analyzed by GC-TCD. The yield of methyl lactate is 50%.

Example 4 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of[N(CH₃)₂(n-C₁₈H₃₇)₂]Cl were added into a reactor (inside volume 12.0 mL)as catalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g ofsucrose were added into the reactor, and then the reactor was sealed andheated to 130° C. under stirring to carry out the reaction (from 25 to130° C. within 25 min) The reaction was carried out at 130° C. for 2 h.The product was analyzed by GC-TCD. The yield of methyl lactate is 43%.

Example 5 Reaction Results of Starch

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of[N(CH₃)₃(n-C₁₄H₂₉)]Cl were added into a reactor (inside volume 12.0 mL)as catalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g ofsucrose were added into the reactor, and then the reactor was sealed andheated to 160° C. under stirring to carry out the reaction (from 25 to160° C. within 25 min) The reaction was carried out at 160° C. for 8 h.The product was analyzed by GC-TCD. The yield of methyl lactate is 35%.

Example 6 Reaction Results of Corn Sucrose

In the reaction, 0.200 g of Sn(CH₃SO₃)₂ and 0.500 g of[N(CH₃)₃(n-C₁₈H₃₇)]Cl were added into a reactor (inside volume 12.0 mL)as catalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g ofsucrose were added into the reactor, and then the reactor was sealed andheated to 130° C. under stirring to carry out the reaction (from 25 to130° C. within 25 min) The reaction was carried out at 130° C. for 2 h.The product was analyzed by GC-TCD. The yield of methyl lactate is 43%.

Example 7 Reaction Results of Sucrose

In the reaction, 100.0 g of SnCl₂.2H₂O and 200.0 g of NH₄Cl were addedinto a reactor (inside volume 10.0 L) as catalyst, and then 3.750 L ofmethanol was added into the reactor. The reactor was sealed and heatedto 130° C. under stirring. 800.0 g of water and 500.0 g of sucrose weremixed to obtain a solution, which was pumped into the reactor with aflow of 8.0 mL/min to carry out reaction. After pumping all of thesucrose aqueous solution, continue 1 more hour at 130° C. to completethe reaction. The product was analyzed by GC-TCD. The yield of methyllactate is 37%.

Example 8 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of quaternaryammonium chloride were added into a reactor (inside volume 12.0 mL) ascatalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g of sucrosewere added into the reactor, and then the reactor was sealed and heatedto 130° C. under stirring to carry out the reaction (from 25 to 130° C.within 25 min) The reaction was carried out at 130° C. for 2 h. Theproduct was analyzed by GC-TCD. The yield of methyl lactate is given inTable 1.

TABLE 1 Reaction results of sucrose H₂O SnCl₂•2H₂O T (g) (g) 0.500 (g) t(h) (° C.) Y (%) 0.200 0.200 [N(CH₃)₃(n-C₁₈H₃₇)]Cl 2 130 59 0.200 0.200[N(CH₃)₃(n-C₁₆H₃₃)]Cl 2 130 49 0.200 0.200 [N(CH₃)₃(n-C₁₄H₂₉)]Cl 2 13047 0.200 0.200 [N(CH₃)₃(n-C₁₂H₂₅)]Cl 2 130 42 0.200 0.200 [N(CH₃)₄]Cl 2130 30 0.200 0.200 N(C₈H₁₇)₃ 2 130 10 0.200 0.200 [N(CH₃)₂(n-C₁₈H₃₇)₂]Cl2 130 43 0.200 0.200 [N(CH₃)₂(n-C₁₂H₂₅)₂]Cl 2 130 35 0.200 0.200[N(CH₃)₂(n-C₁₀H₂₁)₂]Cl 2 130 46

Example 9 Reaction Results of Starch

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of quaternaryammonium chloride were added into a reactor (inside volume 12.0 mL) ascatalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g of starchwere added into the reactor, and then the reactor was sealed and heatedto 160° C. under stirring to carry out the reaction (from 25 to 160° C.within 25 min) The reaction was carried out at 160° C. for 8 h. Theproduct was analyzed by GC-TCD. The yield of methyl lactate is given inTable 2.

TABLE 2 Reaction results of starch H₂O SnCl₂•2H₂O T (g) (g) 0.500 (g) t(h) (° C.) Y (%) 0.200 0.200 [N(CH₃)₃(n-C₁₈H₃₇)]Cl 8 160 37 0.200 0.200[N(CH₃)₃(n-C₁₆H₃₃)]Cl 8 160 34 0.200 0.200 [N(CH₃)₃(n-C₁₄H₂₉)]Cl 8 16034 0.200 0.200 [N(CH₃)₃(n-C₁₂H₂₅)]Cl 8 160 35 0.200 0.200 [N(CH₃)₄]Cl 8160 36 0.200 0.200 N(C₈H₁₇)₃ 8 160 2

Example 10 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of quaternaryammonium chloride were added into a reactor (inside volume 12.0 mL) ascatalyst. 6.0 mL of methanol, 0.200 g of water, and sucrose were addedinto the reactor, and then the reactor was sealed and heated to 130° C.under stirring to carry out the reaction (from 25 to 130° C. within 25min) The reaction was carried out at 130° C. for 2 h. The product wasanalyzed by GC-TCD. The yield of methyl lactate is given in Table 3.

TABLE 3 Reaction results of starch sucrose SnCl₂•2H₂O T (g) (g)[N(CH₃)₃(n-C₁₈H₃₇)]Cl t (h) (° C.) Y (%) 0.200 0.200 0.500 (g) 2 130 590.400 0.200 0.500 (g) 2 130 45 0.600 0.200 0.500 (g) 2 130 44 0.8000.200 0.500 (g) 2 130 43 1.000 0.200 0.500 (g) 2 130 38 1.200 0.2000.500 (g) 2 130 37 2.000 0.200 0.500 (g) 2 130 28

Example 11 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and 0.500 g of quaternaryammonium chloride were added into a reactor (inside volume 12.0 mL) ascatalyst. 6.0 mL of methanol, 0.200 g of water, and sucrose were addedinto the reactor, and then the reactor was sealed and heated to 130° C.under stirring to carry out the reaction (from 25 to 130° C. within 25min) The reaction was carried out at 130° C. for 2 h. The product wasanalyzed by GC-TCD. The yield of methyl lactate is given in Table 4.

TABLE 4 Reaction results of sucrose sucrose SnCl₂•2H₂O T (g) (g)[N(CH₃)₃(n-C₁₆H₃₃)]Cl t (h) (° C.) Y (%) 0.200 0.200 0.500 (g) 2 130 490.400 0.200 0.500 (g) 2 130 45 0.600 0.200 0.500 (g) 2 130 42 0.8000.200 0.500 (g) 2 130 37 1.000 0.200 0.500 (g) 2 130 37 1.200 0.2000.500 (g) 2 130 40 2.000 0.200 0.500 (g) 2 130 35

Example 12 Reaction Results of Sucrose

In the reaction, 0.200 g of Sn(CH₃SO₃)₂ and 0.500 g of quaternaryammonium chloride were added into a reactor (inside volume 12.0 mL) ascatalyst. 6.0 mL of methanol, 0.200 g of water, and 0.200 g of sucrosewere added into the reactor, and then the reactor was sealed and heatedto 130° C. under stirring to carry out the reaction (from 25 to 130° C.within 25 min) The reaction was carried out at 130° C. for 2 h. Theproduct was analyzed by GC-TCD. The yield of methyl lactate is given inTable 5.

TABLE 5 Reaction results of starch H₂O Sn(CH₃SO₃)₂ T (g) (g) 0.500 (g) t(h) (° C.) Y (%) 0.200 0.200 [N(CH₃)₃(n-C₁₈H₃₇)]Cl 2 130 43.34 0.2000.200 [N(CH₃)₃(n-C₁₆H₃₃)]Cl 2 130 39.84

Example 13 Reaction Results of Sucrose

In the reaction, 0.200 g of SnCl₂.2H₂O and NH₄Cl were added into areactor (inside volume 12.0 mL) as catalyst. 6.0 mL of methanol, 0.200 gof water, and sucrose were added into the reactor, and then the reactorwas sealed and heated to 130° C. under stirring to carry out thereaction (from 25 to 130° C. within 25 min) The reaction was carried outat 130° C. for 2 h. The product was analyzed by GC-TCD. The yield ofmethyl lactate is given in Table 6.

TABLE 6 Reaction results of sucrose sucrose SnCl₂•2H₂O T (g) (g) NH₄Cl(g) t (h) (° C.) Y (%) 0.200 0.200 0.100 2 130 45.15 0.200 0.200 0.200 2130 47.5 0.200 0.200 0.300 2 130 38.3 0.200 0.200 0.400 2 130 37.260.200 0.200 0.600 2 130 34.01 0.200 0.200 1.000 2 130 39.6 1.000 0.2000.500 2 130 33.53 1.000 0.200 1.000 2 130 25.1 1.000 0.200 1.500 2 13041.16 1.000 0.200 2.000 2 130 27.38 1.000 0.200 2.500 2 130 26.96

Example 14 Reaction Results in 10 Liter Reactor

In the reaction, 100 g of SnCl₂.2H₂O and 200 g of NH₄Cl were added intoa reactor (inside volume 10.0 L) as catalyst. 3.0 kg of methanol wasalso added into the reactor. The reactor was sealed and heated to 130°C. under stirring. A solution of 0.500 kg sucrose in 0.800 kg water waspumped into the reactor with a flow of 10.0 mL/min to carry out thereaction. After pumping all of the sucrose solution into the reactor,the reaction was kept running for another 1.5 h to complete thereaction. The resulted solution was analyzed by GC and high-performanceliquid chromatography (HPLC). 80.2% of total molar yield of methyllactate and lactic acid was obtained. The reaction was reproduced and atotal yield of methyl lactate and lactic acid of 95.0% was obtained.

Example 15 Reaction Results in 10 Liter Reactor

In the reaction, 50 g of SnCl₂.2H₂O and 100 g of NH₄Cl were added into areactor (inside volume 10.0 L) as catalyst. 3.0 kg of methanol was alsoadded into the reactor. The reactor was sealed and heated to 130° C.under stirring. A solution of 0.500 kg sucrose in 0.500 kg water waspumped into the reactor with a flow of 10.0 mL/min to carry out thereaction. After pumping all of the sucrose solution into the reactor,the reaction was kept running for another 1.5 h to complete thereaction. The resulted solution was analyzed by GC and HPLC. 80.7% oftotal molar yield of methyl lactate and lactic acid was obtained.

Example 16 Reaction Results in 10 Liter Reactor

In the reaction, 33 g of SnCl₂.2H₂O and 70 g of NH₄Cl were added into areactor (inside volume 10.0 L) as catalyst. 3.0 kg of methanol was alsoadded into the reactor. The reactor was sealed and heated to 130° C.under stirring. A solution of 0.500 kg sucrose in 0.500 kg water waspumped into the reactor with a flow of 10.0 mL/min to carry out thereaction. After pumping all of the sucrose solution into the reactor,the reaction was kept running for another 1.5 h to complete thereaction. The resulted solution was analyzed by GC and HPLC. 81% oftotal molar yield of methyl lactate and lactic acid was obtained.

Example 17 Reaction Results in 10 Liter Reactor

In the reaction, 20 g of SnCl₂.2H₂O and 40 g of NH₄Cl were added into areactor (inside volume 10.0 L) as catalyst. 3.0 kg of methanol was alsoadded into the reactor. The reactor was sealed and heated to 130° C.under stirring. A solution of 0.500 kg sucrose in 0.500 kg water waspumped into the reactor with a flow of 10.0 mL/min to carry out thereaction. After pumping all of the sucrose solution into the reactor,the reaction was kept running for another 1.5 h to complete thereaction. The resulted solution was analyzed by GC and HPLC. 71% oftotal molar yield of methyl lactate and lactic acid was obtained.

Example 18 Reaction Results in 10 Liter Reactor

In the reaction, 100 g of SnCl₂.2H₂O and 200 g of NH₄Cl were added intoa reactor (inside volume 10.0 L) as catalyst. 3.0 kg of methanol wasalso added into the reactor. A mixture of 0.500 kg corn powder(containing 71% starch) in 0.500 kg water was added into the reactor andsealed the reactor to carry out reaction at 160° C. for 8 h. Theresulted solution was analyzed by GC and HPLC. 54% of total molar yieldof methyl lactate and lactic acid was obtained.

Example 19 Reaction Results in 10 Liter Reactor

In the reaction, 100 g of SnCl₂.2H₂O and 200 g of NH₄Cl were added intothe reactor (inside volume 10.0 L) as catalyst. 3.0 kg of methanol wasalso added into the reactor. The reactor was sealed and heated to 130°C. under stirring. A solution of 0.500 kg glucose in 0.500 kg water waspumped into the reactor with a flow of 10.0 mL/min to carry out thereaction. After pumping all of the glucose solution into the reactor,the reaction was kept running for another 1.5 h to complete thereaction. The resulted solution was analyzed by GC and HPLC. 64% oftotal molar yield of methyl lactate and lactic acid was obtained.

The above descriptions are only preferred embodiments of the presentinvention, and are not intended to limit the present invention. Anyamendments, replacement and modification made to the above embodimentsunder the spirit and principle of the present invention should beincluded in the scope of the present invention.

What is claimed is:
 1. A catalyst for synthesis of lactic acid and itderivatives, comprising: SnY₂.mH₂O and at least one of NH₄X orquaternary ammonium salts, wherein X and Y are selected from F⁻, Cl⁻,Br⁻, I⁻, CH₃SO₃ ⁻, C₆H₅SO₃ ⁻, CH₃C₆H₄SO₃ ⁻ or CN⁻, m represents aninteger of 1 to
 15. 2. The catalyst for synthesis of lactic acid and itderivatives of claim 1, wherein a cation of the quaternary ammoniumsalts has a general formula of (NR₁R₂R₃R₄)⁺, in which, the R₁, R₂, R₃,and R₄ are alkyl groups with formula of C_(n)H_(2n+1), wherein nrepresents an integer of 1 to
 30. 3. The catalyst for synthesis oflactic acid and it derivatives of claim 1, wherein a mass ratio of theat least one of NH₄X or quaternary ammonium salts to the SnY₂.mH₂O is ina range from 1:2 to 5:2.
 4. A method for synthesis of lactic acid andits derivatives, comprising: providing a mixture, comprising: at leastone carbohydrate-containing raw material, at least one alcohol, at leastone catalyst, and at least one solvent, wherein the catalyst comprisingSnY2.mH2O and at least one of NH₄X or quaternary ammonium salts, whereinX and Y are selected from F⁻, Cl⁻, Br⁻, I⁻, CH₃SO₃ ⁻, C₆H₅SO₃ ⁻,CH₃C₆H₄SO₃ ⁻ or CN⁻, m represents an integer of 1 to 15; and heating themixture to obtain lactic acid and its derivatives.
 5. The method forsynthesis of lactic acid and its derivatives of claim 4, wherein thealcohol is selected from the group consisting of monohydroxyl alcohols,dihydroxyl alcohols, and trihydroxyl alcohols.
 6. The method forsynthesis of lactic acid and its derivatives of claim 5, wherein thealcohol is monohydroxyl alcohol, and the monohydroxyl alcohol isselected from a group consisting of methanol, ethanol, 1-propanol,2-propanol, 1-butanol, 2-butanol, and tert-butanol.
 7. The method forsynthesis of lactic acid and its derivatives of claim 5, wherein thealcohol is dihydroxyl alcohol, and the dihydroxyl alcohol is selectedfrom the group consisting of ethylene glycol, 1,2-propandiol, and1,3-propandiol.
 8. The method for synthesis of lactic acid and itsderivatives of claim 5, wherein the alcohol is trihydroxyl alcohol, andthe trihydroxyl alcohol is glycerol.
 9. The method for synthesis oflactic acid and its derivatives of claim 4, wherein a mass ratio of theat least one alcohol to the at least one carbohydrate-containing rawmaterial is greater than
 1. 10. The method for synthesis of lactic acidand its derivatives of claim 9, wherein a mass ratio of the at least onealcohol to the at least one carbohydrate-containing raw material isgreater than 3:2.
 11. The method for synthesis of lactic acid and itsderivatives of claim 4, wherein the at least one solvent is a polarsolvent.
 12. The method for synthesis of lactic acid and its derivativesof claim 11, wherein the polar solvent is selected from a groupconsisting of water, alcohols, the methyl esters of C8 to C22 fattyacids, or mixtures thereof.
 13. The method for synthesis of lactic acidand its derivatives of claim 4, wherein a reaction temperature of theheating step is between 25 and 200° C.
 14. The method for synthesis oflactic acid and its derivatives of claim 13, wherein the reactiontemperature of the heating step is between 25 and 180° C.
 15. The methodfor synthesis of lactic acid and its derivatives of claim 4, wherein theat least one carbohydrate-containing raw material comprises celluloseand the reaction temperature of the heating step is between 80 and 180°C.
 16. The method for synthesis of lactic acid and its derivatives ofclaim 15, wherein the reaction temperature of the heating step isbetween 100 and 180° C.
 17. The method for synthesis of lactic acid andits derivatives of claim 4, wherein the at least onecarbohydrate-containing raw material comprises starch and the reactiontemperature of the heating step is between 80 and 180° C.
 18. The methodfor synthesis of lactic acid and its derivatives of claim 15, whereinthe reaction temperature of the heating step is between 80 and 160° C.19. The method for synthesis of lactic acid and its derivatives of claim4, wherein the at least one carbohydrate-containing raw materialcomprises sucrose or glucose and the reaction temperature of the heatingstep is between 25 and 180° C.
 20. The method for synthesis of lacticacid and its derivatives of claim 19, wherein the reaction temperatureof the heating step is between 25 and 140° C.